1. Field of the Disclosed Embodiments
This disclosure relates to systems and methods for implementing advanced stripping of image receiving media substrates, including and particularly those substrates involved in any cut-sheet image forming process in an image forming device that includes a pressure nip necessitating an ability to reliably remove the sheets of image receiving media substrate from a conformable belt and/or roller surface.
2. Related Art
Modern image forming devices process nearly countless combinations of compositions of image receiving media and image marking materials for forming images on those image receiving media. It is well recognized in the image forming arts that certain combinations of compositions of the image receiving media and image marking materials introduce particular issues with regard to the image receiving medium handling. For example, in a transfix aqueous inkjet process, an intermediate transfer belt is employed onto which a digital image will be printed using aqueous ink jet print heads. Before the aqueous ink is jetted onto the surface of the intermediate transfer belt, a liquid solution is deposited and dried on the intermediate transfer belt. This liquid solution layer may commonly be referred to as a “skin” layer. The skin layer may primarily consist of a combination of a starch, a surfactant and water.
The skin layer may be applied to the intermediate transfer belt in preparation for the application (jetting) of the aqueous ink on the surface of the intermediate transfer belt in an aqueous ink jetting process to develop the digital image on the intermediate transfer belt. The skin layer facilitates the jetted aqueous ink wetting on the surface of the intermediate transfer belt. The digital image is then produced by jetting the aqueous ink onto the skin layer. The thus-formed aqueous ink jet digital image, including the skin layer according to this process, is then dried to form a transferable digital image on the skin covered surface of the intermediate transfer belt.
The intermediate transfer belt, with the transferrable digital image formed thereon, may then be passed through a conformable transfer nip comprised of an external pressure roller and an internal pressure roller that sandwich the intermediate transfer belt therebetween. Image receiving media substrates, in cut-sheet form, are introduced to the transferrable digital image transfer process at the at the conformable transfer nip where the transferrable digital image consisting of the dried film of jetted aqueous ink and the skin layer is transferred from the intermediate transfer belt to the image receiving media substrates.
One of a number of challenges in effectively employing this process, and other like processes, occurs at the point of the transfer of the transferrable digital image to the image receiving media substrate. Based on a tackiness of the skin layer, the dried film of skin and aqueous ink jet image adheres to the intermediate transfer belt. Additionally, the cut-sheet image receiving media substrate sticks firmly to the dried film, which is adhered to the intermediate transfer belt. The dried film generally extends completely toward, or to, the edges of the image receiving media substrate, regardless of how much of the surface of the image receiving media substrate may receive the actual image. As such, even the leading edge of the image receiving media substrate, with the dried film and image formed thereon, is adhered to the intermediate transfer belt in a manner that renders ineffective certain conventional techniques, methods and system components that are generally employed for stripping cut-sheets of image receiving media substrate from the intermediate transfer belt at an exit of the conformable transfer nip. An air knife, for example, may be generally ineffective because of the strict adherence of the leading edge of the cut-sheet image receiving media to the intermediate transfer belt. In other words, the air knife tends to only be effective in instances in which a leading edge of the image receiving media substrate may lift slightly so as to provide at least a minimal gap between the intermediate transfer belt and the image receiving media substrate. Because the skin goes all away to the edge of the image receiving media, no gap is generally formed at that point.
A relatively well-known type of media handling technology that may be usable to address the leading edge adhering problems associated with certain image receiving media/image marking media combinations involves an adaptation of a technique used in the offset printing industry by employing mechanical “gripper bars.” The adapted technique employs mechanical gripper bar components to physically clamp at least the leading edge (and sometimes the trailing edge) of each sheet of image receiving media generally to drum components in the image receiving media transport path as the sheets of image receiving media are passed through the conformable transfer nip. This positive mechanical control of the leading edge of the individual sheets of image receiving media is intended to ensure that a positive “stripping” force is applied to the individual sheets of image receiving media downstream of the conformable transfer nip to peel the individual sheets of image receiving media away from, for example, a surface of an intermediate transfer belt.
Employment of gripper bars is, however, not without its drawbacks. For example, a fairly major limitation of the gripper bar approach is that devices applying this approach are limited to a fixed pitch. In other words, the spacing of the gripper-bars as mechanical components in the image receiving media transport path is fixed (not variable) to accommodate a maximum image receiving media sheet length in the process direction. This fixed pitch characteristic reduces efficiency in the image forming devices within which this approach is employed, for example, when the image forming device is used to form images on sheets of image receiving media that are smaller, and in cases significantly smaller, in length than the maximum image receiving media sheet length that defines the necessary spacing for the gripper bars, resulting in significant productivity loss. The productivity loss is measurable and particularly proportional to the difference between the maximum image receiving media sheet length and the shorter image receiving media sheet length that is being processed at any given time. Additionally, gripper bar and drum assemblies tend to be very expensive and comparatively large, both of which characteristics tend to be prohibitive for the High-End Cut Sheet or HECS devices and product space. Finally, gripper bar technologies, by their very nature, preclude printing all the way to an edge of the image receiving media substrate, which may preclude the digital image and skin combinations described above.